In the oil production industry a tool is often lowered into a well bore to a depth of several thousand feet by means of a cable. On some occasions the tools become stuck and cannot be brought back up to the rig floor. In such instances, a process termed as "stripping" is undertaken. The cable supporting the tool is clamped above the rig floor in order to prevent the cable from falling into the bore and the cable is cut above the clamp. A special tool termed as an overshot is then secured to a section of pipe and the pipe section is then telescoped downwardly over that portion of the cable above the clamp and the cable is clamped above the pipe section to thus secure the cable in order that the lower clamp may be removed and the pipe section may be allowed to slide downwarly along the cable.
Additional sections of pipe are added to the pipe string by repeated upper and lower clamping of the cable with the result that the string of pipe will be lwered into the well bore around the cable until the overshot at the bottom at the string of pipe comes into contact with and "grabs" the stuck tool. Then, the cable is released from the stuck tool and withdrawn through the pipe and the pipe is then withdrawn from the well together with the overshot and the previously stuck tool supported from the overshot.
However, during the "stripping" process the upper and lower clamping of the cable can malfunction with the result that the cable is dropped and falls downwardly through the pipe and completely through the overshot tool to the bottom of the well bore.
The loss of the cable in the well bore represents a considerable loss in the value of the cable and also results in several thousand feet of cable dropping to the bottom of the well bore and causing considerable problems with future well operation. Accordingly, a need exists for a means whereby accidental dropping of the cable during a "stripping" operation will not result in the cable falling completely through the overshop supporting pipe string and the overshot down into the bottom of the well bore.
Examples of various forms of gripping tools including some of the general structural and operational features of the instant invention are disclosed in U.S. Pat. Nos. 3,011,549, 3,147,809 and 3,358,765. However, these previously patented gripping devices are not capable of performing the function of the structure of the instant invention.